A new radio front end is needed to support a world phone or world tablet type user equipment having three or more antennas that are used to operate in a carrier aggregation mode for many band combinations. For example, the radio front end of a world phone or world tablet is required to support band 7 (B7) of Long-Term Evolution Frequency Division Duplex (LTE FDD) along with bands B38, B40, B41, and B41 Extended Global Platform (XGP) LTE Time Division Duplex (TDD), which covers a bandwidth that ranges from 2300 MHz to 2700 MHz. Several of the bands within the 2300 MHz to 2700 MHz bandwidth have no requirement for carrier aggregation support. Examples of these bands are B7 FDD and TDD bands B38, B40, B41, and B41 XGP. The listed bands requiring diversity RX employ multiple-input and multiple-output (MIMO) techniques that use two receivers. However, it is to be understood that bands involving Global System for Mobile (GSM) and enhanced data rates for GSM Evolution (EDGE) do not require MIMO techniques. Another requirement for world phone or world tablet type user equipment is implementation of an antenna swapping technique that can change which of two antennas is used as a main antenna while the other antenna is used as a diversity/RX MIMO antenna. The antenna swapping technique allows a world tablet type user equipment to select a best antenna for achieving total radiated power (TRP). Yet another requirement calls for a technique that switches between three different antennas for operation in bands between 2300 MHz to 2700 MHz. A downlink frequency range for B7 extends from 2620 MHz to 2690 MHz.
FIG. 1 is a schematic of a related art radio front end 10 that supports world phone/world tablet bands such as those exemplified above along with carrier aggregation and receiver diversity. The radio front end 10 includes transceiver circuitry 12 that outputs second generation (2G), third generation (3G), and fourth generation (4G) low band (LB) and high band (HB) transmit (TX) signals to power amplifier and switch circuitry 14. It is to be understood that the transceiver circuitry 12 includes a plurality of transceivers to cover the various communication modes used by world phone/world tablet type user equipment. A TX filters module 16 receives and filters the LB and HB signals that are amplified and switched by the power amplifier and switch circuitry 14. Diversity antenna switch circuitry 18 is coupled to the TX filters module 16 via transceiver signals paths TRX1-TRX10. Signals conducted by the transceiver signal paths TRX1-TRX10 are routed to at least one of a first antenna A1 and a second antenna A2 through a first diversity antenna port 20 and a second diversity antenna port 22, respectively.
A mixed filter module 24 filters TX signals that pass between ultrahigh band (UHB) switch circuitry 26 and the power amplifier and switch circuitry 14. The mixed filter module 24 also filters RX signals that pass between the transceiver circuitry 12 and the UHB switch circuitry 26. A UHB antenna A3 passes TX and RX signals through a UHB antenna port 28. An alternate RF signal path RF1 is used to route signals between the UHB switch circuitry 26 and the diversity antenna switch circuitry 18.
A diversity switch module 30 routes HB signals and LB signals from the diversity antenna switch circuitry 18 to the transceiver circuitry 12. The diversity switch module 30 includes an HB switch 32 having a pole coupled to the diversity antenna switch circuitry 18 via an HB RF path HB RF2. The diversity switch module 30 also includes an LB switch 34 having a pole coupled to the diversity antenna switch circuitry 18 via an LB RF path LB RF2. The diversity switch module 30 further includes a plurality of filters and diplexers 36 that are coupled to throws of the HB switch 32 and the LB switch 34. RX signals are conducted from the diversity switch module 30 to the transceiver circuitry 12 via receiver RF paths that include diversity receive (DRX) paths, a B7 RX path, and digital cellular service (DCS) receive paths. The B7 RX path includes a B7 filter 38 for filtering B7 RX signals. Both the B7 RX path and the B7 filter 38 are highlighted by bold text and a thick line. A practice of locating the B7 RX path and B7 filter 38 within the diversity switch module 30 is typical of radio front ends such as depicted in the related art radio front end 10. However, passing B7 frequency division duplex (FDD) signals through the HB switch 32 makes it necessary to increase the linearity of the HB switch 32 to a level that is relatively much greater than would be necessary for other diversity signals passed by the HB switch 32. This increased linearity requirement for B7 FDD is at least due in part to a necessity to coexist with the industrial, scientific, and medical (ISM) band. In fact, the linearity for the HB switch 32 requires a relatively very high linearity of around about +79 dBm in order to accommodate B7 FDD signals.
Thus, there is a need for a new radio front end that is configured to allow for a reduced diversity switch linearity requirement to support world phone or world tablet type user equipment having three or more antennas.